1. Field of the Invention
The invention relates generally to navigation mapping systems and, more particularly, to navigation mapping systems that post process GNSS/INS measurement data and camera image data.
2. Background Information
Many navigation mapping systems utilize position, velocity and attitude solutions that correspond to still or video camera images to provide location and other information of interest to users. GIS systems, for example, which provide users with the critical information such as the locations of building entrances, fire hydrants, area trees, and so forth, may rely on photographic or video images of the area and use corresponding GNSS and INS measurement data to determine the locations of the respective features of interest. Route mapping systems, such as systems for providing driving directions, may provide users with images of the end destination, intersections and other points of interest along the route, and so forth, based on the locations of the features as previously calculated using images of the area.
To calculate the locations of the features of interest, vehicles equipped with one or more cameras and a GNSS/INS subsystem travel throughout the area. At designated times, and typically essentially continuously, the one or more cameras take images, e.g., videos, of the area, and the GNSS/INS subsystem saves the GNSS and INS measurement data obtained using a GNSS receiver and the inertial measurement unit (IMU). The images, GNSS measurement data, and the INS measurement data are time tagged, for example, with GNSS time, and the images, and measurement data are saved for later processing, i.e., post processing.
The post processing performed by conventional systems consists of processing the GNSS measurement data and the INS measurement data in a known manner to calculate the position and attitude of the camera for the camera images that correspond in time to the processed measurements. Using the camera position and attitude information, the system determines the locations of features of interest identified in the images in a known manner. For applications in which precise locations are required for the features of interest, high quality, and thus costly, IMUs may be needed in environments in which there is significant signal blockage, such as, for example, certain urban environments. Further, while it is expected that the use of the camera image data in the calculations for position and attitude may help to determine more precise location information in these environments, the calculations become quite time consuming as well as processing intensive.